Sometimes eBay auctions are the only recent price guidance for scarce Tolkien items. I personally try to keep a list of items I haven't seen in a while, so I have some idea what people are willing to pay. Would it be useful to have this kind of database available publically? It could take a lot of storage down the line, so it might require ad support or possibly a small subscription fee (after people have used it for a while and see if it is worthwhile.)

Speaking only from my experience picking up Tolkien calendars on eBay: I'm not certain how good a guide to prices it would be. Some bidders get caught up in the auction and pay more than an item should go for (and I have been on both the winning and losing side of such auctions!) So finding a high price and expecting your item to sell for the same is sometimes not realistic. Conversely, an item might sell for a somewhat (or even drastically) lower price than might be expected. This can occur on an eBay auction for which there is no reserve or a low starting bid yet a limited interest (few collectors). In which case, would you list an item for much less than you "know" it's worth? I have heard from eBay sellers that it is MUCH better to be on the selling side rather than the buying side because of the auction frenzy. So how valuable are those prices when it comes to selling (not auctioning) an item?

And then there is the ebb and flow of interest in collectibles. If I were to sell some of the calendars that I have acquired over the years, I doubt that I would recoup the cost of some (generally uncommon or true rarities) that I acquired at the height of the Tolkien craze created by the movies. So a "Guide to eBay prices" would seem to me to be of limited use as prices can fluctuate wildly in a year or two. For true rarities (as I think you may be limiting your database to), the values may remain useful for some time (the caveats above notwithstanding).

You may disagree, but an item is worth only what someone is willing to pay for it. And the best way to determine that is a simple negotiation between buyer and seller.

I'll break my response into two parts - price guides in general, and then eBay in particular.

Price guides suffer from exactly the issues you bring up. They can only look backwards in time, so can be off quite a bit based on the ebb and flow of popularity and scarcity. But, they are strongest when they track actual sales rather than asking prices, as your mention - a completed transaction (on or off eBay) shows exactly what the market will bear at that one particular moment in time, and that may include quite a bit of hype or none at all. Auction house prices (Sotheby's and Christie's at the high end for example) are definitely used by rare book dealers to price their stock, as are other dealer catalogs and known past sales to a lesser extent. So even a flawed price guide can be useful both to a seller and a buyer to start their negotiations with, at least.

eBay items that are common are quite accurately priced (for successfully completed auctions) because everybody skips the higher priced items and successfully buys a lower priced copy without much effort. Items that are scarce tend to get close to their market value over time, with the occasional hyped sky-high result and the occasional steal. [Note - Unfortunately eBay is not always the right venue for rare items - how many people will drop $15,000 on a first edition set of LOTR based on a few pictures and only a few days to investigate the seller, etc. But those rare items do sell for that price, and regularly, just not usually on eBay.] I guess the point I am making is the most accurate estimate of "what the market will bear" is made when you average past results over time, and for items that don't show up often you typically only have one (or zero) data points to know where the market is.

The auctions I am imagining tracking fall in the scarce category (though I would certainly track rare items that complete sucessfully.) The sort of thing you typically can't do a completed auctions search or ABE search and find a comparible item. Pricing an item too high can prevent the negotiations from even starting, and too low can leave one party (the seller) regretting things. I like both parties to feel quite happy!

I think it would be interesting to see the results over a long period of time. I do agree that ebay may not give an acturate price due to spikes and troughs of individual auctions, these should be averaged out over time.

I would like to compare these results with the prices i have paid for books in my collection.

It would also be interesting to see if any trends (like the increases in prices due to the movies) are occuring